Late-Quaternary environments and human occupation of the south-central Andes

This manuscript focuses on the study of paleoecological history in relation to the process of human occupation and adaptation to the high-altitude puna ecosystem of the south-central Andes. The hypothesized but undocumented Late Pleistocene-Holocene environmental and climatic change are here examined. The present study is based on pollen analysis of a Lateglacial-Holocene sediment section from Laguna Seca, a shallow lagoon in the Chungara-Cotacotani lake district. Overall, the Laguna Seca record indicates the existence of a relatively stable high Puna ecosystem characterized by grassland vegetation since at least 12,000 yr B.P. The year-round presence of open water and occurrence of lowland Yunga-forest pollen during the initial Holocene after 11,000 yr B.P. suggest a climate cooler and moister than today. The decline of arboreal taxa towards about 8000 yr B.P. and increase in grass pollen signals a change in the annual distribution of precipitation and a trend towards drier and probably warmer conditions in the high Puna that becomes established at 7000 yr B.P. At about 5000 yr B.P. a short period of increasing moisture is suggested by a significant increase in pollen of aquatics and Yungas pollen taxa coming into the high Puna. At about 2000 yr B.P. a sharp increase in Compositae tubuliflorae pollen and a decrease in Gramineae is followed by a increase in Cyperaceae and Plantago pollen together with the disappearance of aquatic taxa. This may be interpreted either as a trend towards much drier conditions or as human manipulation of the environment through the first effects of camelid pastoralism. In addition, the Laguna Seca record provided no evidence of over-utilization of the woody Polylepis and Azorella compacta two fuel resources of the high Puna. Whereas vegetational and climatic changes are suggested there is not yet conclusive evidence of a direct link between climate and Middle Archaic culture change in the Dry Puna ecosystem.